These spiders hunt by walking on water, using surface tension like a living web.

Nature · Published 3 October 2026 Swipe more like this →

In short: Fishing spiders of the genus Dolomedes do not build webs to catch their prey. Instead, they use the surface of ponds and streams as a sensory net. By detecting vibrations through their legs, these nocturnal hunters can distinguish between a struggling insect and the background noise of flowing water.

The genus Dolomedes, known as fishing spiders, comprises over 100 species distributed worldwide. While most are semiaquatic, they are defined by their remarkable ability to traverse water surfaces. Their bodies are covered in hydrophobic, velvety hairs that allow them to stand or run on water, effectively using surface tension in the same way other spiders utilize silk webs. When submerged, these hairs trap a layer of air, creating a silvery film that enables the spiders to breathe via their book lungs while underwater.

These spiders are master ambush predators. They wait at the water's edge with their front legs extended, acting as highly sensitive vibration detectors. Equipped with specialized organs called trichobothria, they can pinpoint the location and distance of prey, such as mayflies or even small fish, by interpreting ripples on the water. This tactile sense is so acute that it allows them to ignore environmental noise, like wind or falling leaves, while focusing on the erratic vibrations of struggling insects. Once prey is detected, they sprint across the surface to capture it, sometimes using silk draglines to maintain their position.

The diversity within the genus is significant, with species ranging from the bog-dwelling raft spiders of Europe to the forest-stream specialists of New Zealand. Some species, such as the North American D. tenebrosus and D. okefinokensis, exhibit extreme sexual dimorphism, where males are less than half the size of females. In some cases, mating results in the death of the male. Despite their aquatic prowess, they face threats from birds, snakes, and specialized parasitic wasps, such as Anoplius depressipes, which can dive underwater to paralyze them. Their survival often depends on their ability to retreat beneath the surface, where they remain protected by their air-trapping, hydrophobic coat.

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